Saichania (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia and China. The first fossils of Saichania were found in the early 1970s in the Baruungoyot Formation. In 1977, the type species Saichania chulsanensis was named. Saichania is more robustly built than other members of the Ankylosauridae, measuring 5–7 metres (16–23 ft) in length and 1.4–2.0 metric tons (1.5–2.2 short tons) in body mass. Neck vertebrae, the shoulder girdle, and ribs were fused or firmly connected. Its body is flat and low-slung, standing on four short legs. The forelimbs were very powerful. The head was protected by bulbous armour tiles. It could defend itself against predators like Tarbosaurus with a tail club. On the torso, keeled osteoderms were present. Saichania bit off plants in its desert habitat with a horny beak and processed them in its wide hindgut.
History of discovery
In 1970 and 1971 a Polish-Mongolian expedition found ankylosaurian fossils in the Gobi Desert near Chulsan, or Khulsan. The type species Saichania chulsanensis was named and described by the Polish palaeontologist Teresa Maryańska in 1977, along with the related species Tarchia kielanae. The generic name originates from the Mongolian сайхан (saikhan), meaning "beautiful", referring to the pristine state of preservation of the type specimen. The specific name refers to the provenance near Chulsa. The holotype of Saichania chulsanensis, specimen GI SPS 100/151, was found in a layer of the Barun Goyot Formation, dating from the late Campanian, about seventy-three million years old. It consists of a skull and the anterior part of the postcranial skeleton: seven neck vertebrae, ten back vertebrae, the left shoulder girdle, the left forelimb, the two cervical halfrings and extensive armour in life position. The holotype is largely articulated. Referred specimens include ZPAL MgD-I/114 consisting of an undescribed fragmentary skull roof and associated armour, and an undescribed, almost complete skeleton with skull, specimen PIN 3142/251.
Later, also the juvenile specimen MPC-D 100/1305 was referred and extensively described in 2011, seeming for the first time to provide complete information on the postcranial skeleton. However, in 2014 Victoria Megan Arbour concluded that the describers had been misled by the skeleton having been completed with a skull cast of GI SPS 100/151, and that the remainder of the fossil belonged to some other ankylosaur, possibly Pinacosaurus. On the other hand, Arbour added to the number of possible Saichania specimens by referring PIN 3142/250, a skull previously seen as a Tarchia exemplar. This would imply that Saichania, formerly thought to occur solely in the Barun Goyot Formation at Khulsan, is also known from the Nemegt Formation at Khermeen Tsav. Saichania would then be the only ankylosaur definitely known from the Nemegt, its occurrence thus spanning the time of the Campanian–Maastrichtian transition, and early Maastrichtian (Nemegtian) period. Arbour also considered the Chinese taxa Tianzhenosaurus youngi Pang & Cheng 1998 and Shanxia tianzhenensis Barrett, You, Upchurch & Burton 1998 to be junior synonyms of Saichania. The referral of PIN 3142/250 to Saichania was contested by Penkalski & Tumanova who considered this specimen to be referable to a new species of Tarchia, T. teresae.
Description
Size, build and distinguishing traits
Saichania was a medium-sized ankylosaur, measuring 5–7 metres (16–23 ft) in length and 1.4–2.0 metric tons (1.5–2.2 short tons) in body mass. Finds of tail clubs of gigantic individuals suggest larger sizes but their reference to Saichania cannot be substantiated as the holotype, the only specimen sufficiently described, only consists of the front of the animal. Saichania shared the general ankylosaurid build, being a low-slung, broad, heavily armoured dinosaur, with short forelimbs. Even for an ankylosaurid however, Saichania is exceptionally robust, its rump strengthened by ossifications and fusions of the vertebral column, ribs, shoulder girdle and breast bones. Arbour in 2014 established a revised list of distinguishing traits. The osteoderms on the skull are bulbous. The first and second neck vertebrae are fused into a single element, a syncervical. The upper side of the humerus is very broad, equalling 70% of the total length of the bone. The rib shafts are expanded by intercostal ossifications, the cartilage connecting the ribs having been turned into bone sheets. The cervical halfrings, protecting the neck, have each an underlying continuous band of bone and the borders between the segments of these rings are covered by extra armour plates entirely hiding these connections from view.
Skull The skull of Saichania is broad, 455 millimetres long and 480 millimetres wide with the holotype. The top of the snout is covered with strongly convex osteoderms. These armour tiles on the snout comprise a central large caputegula. A large "loreal" osteoderm covers much of the top edge and the side of the snout. The caputegula on the prefrontal is of moderate size and not strongly protruding sideways. The osteoderms on the upper eye socket rim are continuous, not forming two peaks. An extra osteoderm on the rear supraorbital, as in Tarchia, is lacking. The pyramid-shaped squamosal horns on the rear skull corners are broad, not narrow as with Tarchia. These horns have a uniform surface texture, not a division into a smooth and rough surface as in Zaraapelta. On the cheek, large triangular quadratojugal horns are present.
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